Once World War I had been declared, the gloves were off; the challengers to
Britain's power, previously unidentified in films, were now named outright, as
in the title of this film, and in Huns of the North Sea (1914) and The
Kaiser's Spies (1914).

The German Spy Peril is an inspired piece of propaganda, drawing parallels
with the gunpowder plot and referencing the surge in patriotic enlistment to the
armed forces. Reviews at the time called it "[a] most exciting and thoroughly
topical subject". The hero of the film tries to enlist in the army but, due to
ill-health, is rejected. Overhearing German spies planning to blow up the Houses
of Parliament, he determines to prevent them, crying "We will die together, you
German dogs, for my King and my country's sake." Shots of Big Ben counting down
the minutes and standing after the explosion add authenticity and a sense of
dramatic tension.